Field of the Invention
The present invention relates to an imaging apparatus and an imaging system.
Description of the Related Art
A stacked imaging apparatus described in Japanese Patent Application Laid-Open No. 2010-16594 has a structure in which a photoelectric conversion layer is formed above a semiconductor substrate in which a pixel circuit such as a charge accumulating unit is formed, with an insulating layer therebetween. A lower electrode in the photoelectric conversion layer and the pixel circuit formed in the semiconductor substrate are electrically connected by a contact wiring or the like.
Japanese Patent Application Laid-Open No. 2010-16594 discloses a structure of adjusting the potential of a connection unit (a diffusion region 3 connected to the lower electrode in the photoelectric conversion layer) and the potential of a potential barrier unit (a region below a gate 7a of a transistor for transferring a charge) to the same potential when exposure starts. This solves a problem in that part of the charge generated in the photoelectric conversion layer remains in the connection unit. The potential of the potential barrier unit is adjusted to a potential predetermined by a potential determination mode. The potential determination mode is a mode of repeatedly checking, while changing the gate potential, whether or not dark current is output, and is described as being used in an adjustment process in an imaging apparatus manufacturing facility and the like in Japanese Patent Application Laid-Open No. 2010-16594.
In an imaging apparatus using a buried photodiode formed in a substrate, the buried photodiode can be fully depleted, i.e. can fully discharge the charge accumulated therein by photoelectric conversion. Accordingly, when transferring a signal from the buried photodiode to a charge detection unit, full charge transfer is possible. Therefore, no kTC noise associated with charge transfer occurs. In the structure of the stacked imaging apparatus as in Japanese Patent Application Laid-Open No. 2010-16594, however, the charge is not fully transferred, and kTC noise may occur when turning off a transistor of the potential barrier unit after the charge transfer.
To reduce such kTC noise, the potential of the potential barrier unit needs to be adjusted according to the amount of signal generated in the photoelectric conversion layer of each pixel. However, with the potential adjustment method by the potential determination mode described in Japanese Patent Application Laid-Open No. 2010-16594, it is difficult to adjust the potential according to the amount of signal generated, upon reading the signal. The structure and reading method described in Japanese Patent Application Laid-Open No. 2010-16594 thus have a problem of lower image quality caused by kTC noise during charge transfer and the like.